1. Field of the Invention
The present invention relates to a sectional image photography system and method thereof for examining an inner portion of an examined object which can not be seen with the naked eye, by obtaining a sectional image of the examined object.
2. Description of the Related Art
Generally, quality inspections are carried out with respect to mass-produced products to check possible abnormalities of the products. With respect to the object whose abnormality can not be checked with the naked eye such as soldered parts of electronic components mounted on a printed circuit board, for example, the quality inspection is carried out through a radiation sectional image such as an X-ray sectional image (hereinafter commonly called X-ray sectional image). The quality inspection through the X-ray sectional image is carried out by a sectional image photography system shown in FIG. 1, which is a special-purpose machine for the quality inspection.
As shown in FIG. 1, the such a conventional system includes a mounting table 10, an X-ray projector 20, an image multiplying tube 30, a view selector 40, and a camera 50. As shown in FIG. 2, the X-rays are projected from the X-ray projector 20 rotatably along a circumference of the X-ray projector 20 at a constant speed. The X-rays are then transmitted through an examined object E which is loaded on the mounting table 10. The X-rays are transmitted through the examined object E into visible images on the image multiplying tube 30.
Here, as shown in FIG. 2, the partial images are formed on different locations on an image surface 32 of the image multiplying tube 30 in accordance with the respective X-ray projecting locations. The partial images on the respective locations are the result of the X-rays which are projected and transmitted from different directions, and by combining these partial images with a certain method, an X-ray sectional image of an arbitrary section of the examined object E is obtained.
Since the X-rays are rotatably projected from the X-ray projector 20 along the circumference thereof, the partial images are also rotatably formed on the image surface 32 of the image multiplying tube 30 in a circumferential direction. Accordingly, the view selector 40 selects the partial image on the image surface 32, and the camera 50 obtains the partial images.
Here, the view selector 40 guides the image formed on a certain location on the image surface 32 to the camera 50 by using a pair of mirrors, and the typical examples thereof are disclosed in the U.S. Pat. No. 4,926,452 granted to Baker et al. and assigned to the Four PI Systems Corporation, and the U.S. Pat. No. 5,594,770 granted to Bowles et al. and assigned to the ThermoSpectra Corporation.
According to the view selector of the U.S. Pat. No. 4,926,452, as shown in FIG. 3, a pair of slanted mirrors 42a and 42b are opposed to each other to transmit the image on the image surface 32 to the camera 50, while being rotated at the same speed with the images which are sequentially formed on the image surface 32 along the circumference of the image surface 32. According to the ThermoSpectra Corporation, as shown in FIG. 4, a pair of mirrors 44a and 44b are disposed under the image multiplying tube 30 to be rotated about X and Y axes, respectively. As the partial images are sequentially formed on the respective locations on the image surface 32, the pair of mirrors 44a and 44b are rotated about X and Y axes so as to select the partial image in a certain area on the image surface 32. Accordingly, the partial images on the image surface 32 are reflected against the pair of mirrors 44a and 44b sequentially, and obtained in the camera 50. Meanwhile, in FIG. 4, the reference numerals 43 and 45 refer to motors for rotating the pair of mirrors 44a and 44b. 
The structure of the conventional sectional image photography system that uses the image multiplying tube 30 in a manner that a plurality of partial images formed on the image multiplying tube 30 are selected by the view selector 40 and then obtained by the camera 50, however, results in a disadvantage of having an image distortion according to the respective X-ray image formative locations on the image multiplying tube 30. Further, the view selector of the U.S. Pat. No. 5,594,770 has more serious distortion since an incident angle of optical axis is varied in accordance with the image formative locations.
If the image distortion is occurred, the clear sectional image of the examined object can not be obtained. Accordingly, there is a process of compensating the distortion of the image by a separate software before combining the partial images obtained by the camera 50, hindering accurate controlling of the sectional image photography system.
In addition to the disadvantage of image distortion mentioned above, the conventional system also has a disadvantage of having complex structure and high possibility of mechanical troubles since the conventional system employs a driving part for driving the view selector, i.e., a pair of mirrors 42xe2x80x2, 44xe2x80x2 and 42xe2x80x3, 44xe2x80x3 for selecting a plurality of partial images formed on the image surface of the image multiplying tube 30.
The present invention has been developed to overcome the above-mentioned problem of the related art, and accordingly, it is an object of the present invention to provide a sectional image photography system and method thereof capable of preventing a distortion of an X-ray image transmitted through an examined object.
Another object of the present invention is to provide a sectional image photography system and method thereof requiring a reduced number of parts, thus, having a simplified structure and an improved reliability.
The above object is accomplished by a sectional image photography system, according to the present invention, including: a mounting table adapted to receive an object to be examined; a radiation projector for projecting a radiation toward an object being examined, the radiation being projected at a same level from different locations; a plane radiation detector for obtaining a plurality of partial radiation images formed from the radiations transmitted through the object in the form of electrical image signals; and an image processor for composition-processing the partial radiation images obtained by the plane radiation detector into a sectional image of a desired section of the object.
According to the preferred embodiment of the present invention, the radiation is an X-ray.
The plane radiation detector may includes one, or a plurality of plane radiation detectors. When the one plane radiation detector is employed, the one plane radiation detector is mounted on an XY table and is moved to correspond to the image formative locations of the radiation images of the radiations projected from the respective locations of the radiation projector and are transmitted through the object. When the plurality of plane radiation detectors are employed, the plane radiation detectors are disposed to correspond to the radiation projected from different locations of the radiation projector. It is preferable that a number of the plane radiation detectors ranges from 4 to 8. More preferably, one more plane radiation detector is vertically disposed below the mounting table.
The image processor includes: a computer; and a frame grabber for converting image signals obtained by the plane radiation detector into image data which can be processed by the computer, and for inputting the image data into the computer.
Meanwhile, the above object is accomplished by a method for obtaining sectional image by using a sectional image photography system according to the present invention, including the steps of: a) placing an object to be examined on a mounting table of the sectional image photography system, and focusing a certain section of the object at a certain height at a focus surface of the sectional image photography system; b) projecting radiations generated from a radiation projector with respect to the object from at least two locations on a circumference of the radiation projector; c) obtaining at least two radiation partial images transmitted through an object being examined in the form of electrical image signals by using a plane radiation detector; and d) obtaining the sectional image by processing at least two radiation image signals which are obtained by the plane radiation detector.
Accordingly, by using the plane X-ray detector to obtain the X-ray images formed from the X-rays transmitted through the examined object, there is no image distortion. Further, when using a plurality of plane X-ray detectors, the structure of the sectional image photography system is simplified while the reliability thereof is improved since there is no need to employ a separate driving part.